Referring to FIGS. 1 and 2, a conventional convertible hand truck includes a truck frame 11 for loading, a toe plate 14 transversely disposed on an end of the truck frame 11, a first wheel unit 12 with two wheels 121 disposed adjacent to the toe plate 14, a second wheel unit 13, and a push handle 15. The second wheel unit 13 includes two wheel supports 132 each connected to the first wheel unit 12 and the truck frame 11 respectively through an extensible frame 133 and a pivotable link 134 for supporting a roller 131. The extensible frame 133 includes extensible outer and inner tubes 135, 136 so as to permit movement of the wheel supports 132 relative to the first wheel unit 12. Thus, the hand truck is convertible between a reclined hand truck state (see FIG. 1) and a platform cart state (see FIG. 2). The push handle 15 has a handle body 151 connected to the truck frame 11 through a pivotable support 152 and having a handgrip end 154 and a sliding end 153. The sliding end 153 is slidably engaged in a guiding rail 111 of the truck frame 11 such that the push handle 15 is movable relative to the truck frame 11 between a retracted position (see FIG. 1) and an extended position (see FIG. 2) for facilitating gripping during the use of the hand truck as a platform cart.
However, since the truck frame 11 in the reclined hand truck state is supported by the pivotable link 134 which is pivotably connected to both the truck frame 11 and the wheel support 132, the truck frame 11 tends to collapse due to the loading thereon and undesirably switch to the platform cart state, thereby causing damage to the loading and injury to a user. Additionally, in the reclined hand truck state, the push handle 15 is retracted into the truck frame 11 and is not extendable from the truck frame 11 to elongate the length of the loading area.